Convergence yoke cores for cathode-ray tubes

ABSTRACT

In a convergence yoke core comprising a pair of L-shaped core members disposed in a U-shaped configuration with their inner ends of shorter legs opposed to each other with a gap therebetween and a static magnet disposed above the gap, the gap is bridged by a magnetic member having positive thermal expansion coefficient or negative thermal coefficient of permeability so as to compensate for the variation in the magnetic flux of the static magnet caused by the variation in the ambient temperature.

United States Patent Inventor Hiroshi lkeuchi Yokohama City, Japan Appl. No. 54,384

Filed July 13, 1970 Patented Nov. 23, 1971 Assignee Denki Onkyo Company, Limited Tokyo, Japan CONVERGENCE YOKE CORES FOR CATHODE- RAY TUBES [56] References Cited UNITED STATES PATENTS 3,325,757 6/1967 Gang 335/217 FOREIGN PATENTS 716,216 8/1965 Canada 335/217 Primary Examiner-G. Harris Attorney-Chittick, Pfund, Birch, Samuels & Gauthier ABSTRACT: In a convergence yoke core comprising a pair of L-shaped core members disposed in a U-shaped configuration with their inner ends of shorter legs opposed to each other with a gap therebetween and a static magnet disposed above the gap. the gap is bridged by a magnetic member having positive thermal expansion coefficient or negative thermal coefficient of permeability so as to compensate for the variation in the magnetic flux of the static magnet caused by the variation 8 Claims, 3 Drawing Figs.

US. Cl 335/212, 335/217 Int. Cl H011 1/00 Field of Search 335/210, 21 l, 212, 217

in the ambient temperature.

PATENTEUunv 23 men 3,623,151

- lOb lOb INVENTOR IIIROSHI IKEUCHI BYB ATTORNEY BACKGROUND OF THE INVENTION This invention relates to an improved convergence yoke core for a cathode-ray tube for color television receivers, for

example.

A prior art convergence yoke core comprises a pair of L- shaped core members which are arranged in a letter U-configuration with their corresponding legs spaced apart a predetermined gap. The free ends of the other legs are disposed on the neck portion of a cathode-ray tube and a static magnet is disposed above the gap between core mem bers to provide the required static operation.

Usually a ferrite magnet is utilized as the static magnet but, different from the ordinary metallic magnet, the temperature coefficient of the ferrite magnet tends to vary with the ambient temperature. More particularly as the ambient temperature rises the residual flux density of the magnet decreases.

In color television receivers, the temperature of the portions 2 of the convergence yoke often rises to about 70 C. by eddy current loss and heat radiation from heat sources in the receiver. For this reason,*even when the static convergence is adjusted to an appropriate condition at the commencement of the operation of the receiver, the static convergence will be disturbed by the temperature rise created during the operation of the receiver, thus requiring subsequent readjustment of the static convergence.

It is therefore an object of this invention to provide a novel convergence yoke core which is not affected by the variation in the ambient temperature.

According to one aspect of this invention the gap between corresponding legs of the core members is bridged by a magnetic member having positive thermal expansion coefficient.

According to another aspect of this invention the gap is bridged by a magnetic member having negative thermal coefficient of permeability. In both cases, the magnetic member is interposed in the gap or bonded to at least one side of the core members. When the flux generated by the static magnet decreases due to temperature rise, the flux shunted by the magnetic member is also decreased to maintain constant the efi'ective flux supplied to the cathode-ray tube.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION THE PREFERRED EMBODIMENTS With reference to FIG. 1 there is shown one embodiment of this invention comprising a pair of letter L-shaped ferrite core members a and 10b which are disposed in a letter U-configuration with their corresponding legs (shorter legs) opposed to each other with a predetermined gap therebetween. In the gap, there is disposed a piece 11 of a copper or aluminum material having positive thermal expansion coefficient and the opposite sides of the piece I! are suitably bonded to the inner ends of the shorter legs of core members 10a and 10b to form a core of U-shaped configuration. At a predetermined distance above the gap is disposed a rotatable static magnet 12 thus completing a convergence yoke core. The outer ends of the longer legs of the core members are slanted to fit about the neck portion of a cathode-ray tube, not shown. Actually, three such cores are disposed about the neck portion at an angular spacing of 120".

In operation, at the commencement of operation of the color television receiver the static convergence is adjusted to the desired condition. When the residual flux density of the static magnet 12 decreases owing to the rise in the ambient temperature the piece 11 expands with the temperature rise. This means increase of the gap width between the inner ends of the shorter legs of the pair of L-shaped core members and 10b.

Assuming now that D, represented the effective flux extending through the neck portion of the cathode-ray tube across outer ends of the longer legs of the core members 10a and 10b and that represents the flux passing through piece 11 or the gap between the inner ends the shorter legs. As the piece 11 expands in response to the temperature rise to increase the gap width the magnetic reluctance of the gap is increased to decrease flux 15. Assuming constant magnetomotive force of magnet 12, decrease in flux Q, results in the corresponding increase in the effective flux 4 In other works as the flux of the static magnet 12 decreases owing to the temperature rise flux 4 decreases so that by the suitable selection of the gap width decrease in the flux of magnet 12 can be compensated for by decrease of flux I Hence the effective flux 9, is always maintained constant irrespective of the decrease in the flux of magnet 12. Since flux 1 provides the required static convergence, once the static convergence of the receiver has been adjusted to the desired condition, this condition would never been disturbed by the temperature rise during operation. Further, as the premeability of L-shaped core members 10a and 10b also tends to decrease with temperature rise it is advantageous to select the gap width of the U-shaped core in due consideration of such decrease in the permeability.

In the modified embodiment of this invention shown in FIG. 2, instead of placing piece 11 of positive thermal expansion coefficient in the gap between the inner ends of the shorter legs of core members 10a and 10b, strips 11' of a copper or aluminum material of positive thermal expansion coefiicient are bonded on the opposite surfaces of shorter legs of L- shaped core members and 10b to form a core of U-shaped configuration. As before the rotatable static magnet 12 is positioned above the gap at a predetermined distance. Alternatively, as shown in FIG. 3, the strip 11 may be applied on only one side of the inner legs or may be wound to embrace both shorter legs as shown in FIG. 2. It will be clear that the modified embodiment shown in FIG. 2 operates in the same manner as the first embodiment.

Further the strip of piece 1 1' may be made of a material for example thermalloy or monel metal, having negative thermal coefficient or permeability. In this case as the flux of magnet 12 decreases in response to temperature rise, the permeability of the piece 11' decrease whereby to increase its magnetic reluctance to decrease flux b Again the effective flux I can be maintained substantially constant irrespective of the variations in the ambient temperature.

In this manner even when the static magnet l2is made of ferrite having poor temperature coefficient it is possible to always maintain the static convergence of a color television receiver at the best condition irrespective of the variation in the ambient temperature.

While the invention has been shown and described in terms of some preferred embodiments thereof it will be understand I that many changes may be made without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

1. A convergence yoke core for a cathode-ray tube comprising a pair of core members of a predetermined configuration, corresponding one ends of said core members being spaced apart a predetermined gap and the other corresponding ends of said core members being also spaced apart to supply magnetic flux to said cathode-ray tube, a static magnet positioned above said gap and a magnetic member disposed to bridge said gap, said static magnet having a tendency to vary its flux according to the variation in the ambient temperature and said magnetic member having characteristic to compensate for said variation of the flux of said static magnet whereby to maintain the flux across said other ends of said core members at a substantially constant value.

2. The convergence yoke core according to claim I wherein said magnetic member has positive thermal expansion coefficient.

said magnetic member is interposed between and bonded to said corresponding one ends of said core members.

7. The convergence yoke core according to claim 5 wherein said magnetic member is bonded to at least one side of said core members to bridge said gap.

8. The convergence yoke core according to claim 1 wherein said core members have generally L-shaped configuration and are disposed in U-shaped configuration.

i l i 2 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent ML 3 ,623,l5l Dated November 23, 1971 Invencofl hJ. Ikeuchi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 42, change "of piece 11 to 11' or piece ll Signed and sealed this 3rd day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

Commissioner of Patents 

1. A convergence yoke core for a cathode-ray tube comprising a pair of core members of a predetermined configurati on, corresponding one ends of said core members being spaced apart a predetermined gap and the other corresponding ends of said core members being also spaced apart to supply magnetic flux to said cathode-ray tube, a static magnet positi oned above said gap and a magnetic member disposed to bridge said gap, said static magnet having a tendency to vary its flux according to the v ariation in the ambient temper ature and sai d magnetic member having characteristic to compensate for said variation of the flux of said static magnet whereby to maintain the flux across said other ends of said core mem bers at a substantially constant value.
 2. The convergence yoke core according to claim 1 wherein said magnetic member has positive thermal expansion coefficient.
 3. The convergence yoke core according to claim 2 wherein said magnetic member is interposed between and bonded to said corresponding one ends of said core members.
 4. The convergence yoke core according to claim 2 wherein said magnetic member is bonded to at least one side of said core members to bridge said gap.
 5. The convergence yoke core according to claim 1 wherein said magnetic member has negative thermal coefficient of permeability.
 6. The convergence yoke core according to claim 5 wherein said magnetic member is interposed between and bonded to said corresponding one ends of said core memb ers.
 7. The conve rgence yoke core according to claim 5 wherein said magnetic member is bonded to at least one side of said core members to bridge said gap.
 8. The convergence yoke core according to claim 1 wherein said core members have generally L-shaped configuration and are disposed in U-shaped configuration. 